A major feature of LTE-Advanced (Long Term Evolution-Advanced or LTE-A), as part of Release 10 of the LTE specification by the 3rd Generation Partnership Project (3GPP), is increased support for multi-user MIMO (multi-input multi-output) in which spatial multiplexing is used to provide separate downlink and uplink communications paths between a base station (referred in LTE systems as an evolved Node B or eNB) and multiple terminals (where a terminal is referred to in LTE systems as user equipment or UE). As more UEs are scheduled per subframe for multi-user MIMO operations, the demand for physical downlink control channel (PDCCH) resources to provide scheduling for physical uplink control channel (PUCCH) resources is increased. The design of the PDCCH in Releases 8/9/10 of the LTE specification provides for a maximum PDCCH size of three OFDM (orthogonal frequency division multiplexing) symbols which is inadequate for meeting this increased demand. Consequently, a new PDCCH design, referred to an enhanced PDCCH (ePDCCH), was introduced in the PDSCH (physical downlink shared channel) region for Release 11 of the LTE specification. The structure of the PDCCH is based upon so-called control channel elements (CCEs), while the ePDCCH uses a design based upon physical resource blocks (PRBs) in order to increase capacity and enhance support for inter-cell interference coordination (ICIC) in heterogeneous network scenarios. The limitation of the Release 8/9/10 PDCCH design for performing inter-cell interference coordination (ICIC) stems from the fact that, due to PDCCH interleaving, the CCEs used for the transmission of downlink control information (DCI) formats in the PDCCH are distributed over the entire bandwidth in an irregular fashion. Placing the ePDCCH in the PDSCH region with a PRB-based scheme, on the other hand, allows the ePDCCH to be distributed over the bandwidth so as to better support frequency-domain ICIC.
The use of the PRB-based ePDCCH, however, cannot be used in the same manner as the CCE-based PDCCH to dynamically allocate uplink resources for acknowledging downlink data transmissions. That is a concern of the present disclosure.